DIPTERA BRACHYCERA. 373 



mention of them seems desirable. These are the six- 

 legged, non-changing Lepismas, the Spring-tails, the 

 Lice, and the Bird-lice. These have been variously 

 arranged ; at one time with the eight-legged Acari, &c., 

 among the Arachnida at another, with the Fleas in the 

 order " Aptera," and so on. 



Whilst, however, the Flea, although apterous, is clearly 

 shown by the nature of its transformations to belong 

 to the true insects, the Spring-tails, Lice, &c., are 

 excluded from this class by the total absence of trans- 

 formations, and have been formed into a class by 

 themselves under the name Ametabola. 



This, again, is divided into Thysanura and Anoplura. 



To the first belongs the little silvery fish-like Lepisma, 

 whose delicate scales are well known to microscopists as 

 a low test object The abdomen is furnished with several 

 bristle-like tails, of which three are the most conspicuous; 

 the mouth is mandibulate, the antennae are long and 

 bristle-like, and without the tail it measures about one- 

 third of an inch. 



The Podura, or Spring-tail, in the same section, is 

 a very curious little creature, effecting its spring by 

 means of a forked tail turned under the abdomen, and 

 acting precisely like the wood-and-catgut spring of the 

 wooden frog made for children. It is smaller than the 

 Lepisma, dark and velvety, with the thorax and abdo- 

 men tolerably distinct, and has large, thick antennae 

 and mandibles. 



These insects are found among wood, in the sawdust 

 in cellars, under stones, &c. 



Anoplura contains the Sucking Lice, Pediculi, and the 

 Nirmi, or Biting Lice, which, except one species which 

 infests dogs, seem to be confined to birds. The Pediculi 



